The present invention relates to a housing of a receiver for personal radio paging service in the VHF band and its receiving antenna structure.
Various types of receiving antennas are employed for miniature radio receivers in view of the frequency bands used and the uses and shapes of the receivers. For use in the HF band and the lower frequency bands the receiving antenna usually takes the form of a wire hanging from the receiver, an earphone cord or a form in which a coil is wound around a rod of ferrite. For use in the VHF, UHF and quasi-microwave bands a U-shaped antenna formed by bending a rectangular plate twice 90.degree. each has been employed conventionally as a loop antenna as disclosed in U.S. Pat. No. 3,436,591 and U.S. Pat. No. 4,814,776. In further miniaturizing the receiver for personal radio paging service in the VHF band into a card form for use as a microminiature receiver which does not use the earphone but has a calling buzzer or an information display such as a liquid crystal display, it is difficult, due to dimensional restrictions, to incorporate the antenna into the receiver housing. Moreover, the U-shaped loop antenna is suitable for use in the frequency bands above 400 MHz and in the state in which it is not significantly affected by the surrounding conditions and held at a certain distance from the human body; however, in case of applying such a loop antenna to a microminiature receiver for personal radio paging service which is used in the VHF band and is usually carried in the user's pocket, bag or handbag, an increase in the quality factor of the antenna, intended for increasing its effective gain despite of its miniaturization, will make the antenna susceptible to the influence of the surrounding conditions, in particular, the influence of the human body, and if the quality factor is reduced so as to lessen the influence, the receiving sensitivity will become so low as not to be practicable. In other words, the conventional loop antenna constitutes a serious obstacle to the microminiaturization of the receiver. Accordingly, the miniaturization of the antenna is the most important problem yet to be solved in the implementation of a thin card-shaped microminiature receiver for personal radio paging service although microminiature electronic circuits such as an LSI and a battery are readily available.